Trays

"Whitening trays are one of the most popular methods of whitening your teeth," Smigel says. "This is also the most practical and price-friendly for patients on a budget. What's great about this whitening method is its ability to remove some mild, intrinsic stains within the tooth enamel, and whiten naturally yellowing teeth." Expect your teeth to go at least three shades whiter than your natural color.

Tray-based systems, available over the counter or from a dentist, involve filling a tray with a gel whitening formula. (Typically, the bleaching agent is hydrogen peroxide.) You'll wear the tray for anywhere between a couple of hours per day to overnight. Fit is key, of course, and over-the-counter trays aren't as precisely measured. "Unlike over-the-counter mouthpieces, professional whitening trays are only custom fitted by a dentist, so that the tray fits comfortably and protects your gums and soft tissue," Smigel notes.

Most kits deliver full whitening benefits between two and four weeks — and it's important to have realistic hopes. "Although a dentist's bleaching gel is more powerful than over-the-counter products, professional at-home whitening treatments can't remove iron deposit stains or the deep, intrinsic stains caused by antibiotics or deep fluoride discolorations," Smigel notes. Another precaution: the powerful gel can be toxic if swallowed, so be careful if using trays overnight or for a prolonged period. "Often, people use at-home treatments indefinitely. That can lead to over-bleaching and permanent damage to the enamel, and it can harm gums," Smigel says. So, if you're thinking of wearing a tray indefinitely... don't.

Rembrandt 2 Hour Whitening Kit, $19.97, available at Walmart.